Conventional gas analyzers have been used to continuously measure the concentration of water or other condensable material in a gas stream. By measuring the types and quantities of gases in an exhaust gas stream of a boiler, one can determine the efficiency of the boiler in burning to completion all the fuel that is being used. By measuring the sensible energy content and chemical energy content of materials remaining in the flue gas and comparing that with the amount of the fuel actually used in the boiler one can evaluate the overall efficiency of the boiler as a heat-producing device.
Whether it is in the context of boiler efficiency or simply an environment where the amount of condensable fluid is a parameter which should be measured, various methods have been proposed for this type of analysis. For example, in the U.S. Pat. No. 3,229,502 to Pappas et al, issued on Jan. 18, 1966, there is disclosed a gas condensation pressure analyzer. The device disclosed relates to a process for determining the concentration of a selected condensable component of gas. The analyzer relies on the measurement of the total pressure required for condensation equilibrium between the sample gas and the condensed component at constant temperature conditions. The system to accomplish this includes a control valve that causes the total gas pressure to oscillate so as to cause a partial pressure of the analytically desired component to seek its vapor pressure. In the Pappas et al. system condensation is accomplished within a restriction or capillary maintained at a constant temperature by a cold bath. The sample gas is delivered directly to the constant temperature bath through a control valve, and once cooled the gas exits the bath through a discharge line.
Another example of a system for determining concentration of vapors in a flowing stream is U.S. Pat. No. 4,507,875, issued to Hirsch et al., on Apr. 2, 1985. The Hirsch et al. patent discloses an apparatus for determination of concentration of water vapor in the exhaust air of a drier used to dry tobacco. The system includes a gas evacuation conduit for receiving a sample of gas from the stream, a gas condenser in the evacuation conduit for condensing out essentially all condensable vapors in the sample and a gas flow meter connected to the gas discharge of the gas condenser for determining the flow of dry gas sample exiting the condenser. The vapor concentration determination is accomplished by sampling a gas line and directing the sample to a condenser, an electric compressor, kept at a temperature of about 5.degree. C. so that the condenser will condense out all of the components of the flow of process gas.
Systems of the type discussed above suffer from many deficiencies. For example, it is often difficult to obtain an accurate measure of the flow rate due to materials existing in the gas which adversely affect the flow measuring equipment. Furthermore, the measuring steps are not conducted in a manner which insures that only flow rates of the desired materials are measured and that unwanted condensation is not obtained. The environment in which the measurements are made is not controlled sufficiently to provide reliable readings. Particularly where comparative readings are involved absence of controlled environments can adversely affect any comparison.
The invention described herein overcomes many of the problems which occur in the systems described above. For example, the sample is drawn initially through a first oven where organics and other materials are condensed and filtered out before the sample is directed to a measuring device. After this initial filtering step the sample is raised to a higher temperature in a second oven to insure that no further condensing occurs when an orifice is used to measure the flow rate of the material before it is subjected to a component removal system which could be an absorption system or a condensing system such as an ice bath. After having the component of interest removed the gas sample is again passed through a second orifice in the same oven as the first orifice to measure the flow rate of the remaining gas. These flow rates are compared to arrive at a percentage of water or other material within the gas. The gas can then be directed through a conventional dry basis gas analyzer to analyze the amount of various remaining components in the gas.